The integrity of components such as valves, fittings or vessels used for gas chromatography or other analytical systems is an important factor in the precision as well as the security of such systems. These components therefore need to be tested prior to installation and periodically once in use to detect the presence of any leaks through the component so that appropriate action can be taken.
Manners of detecting a gas leak in a component include detection with a carrier gas and a tracer gas. For example, it is known in the art to use helium as a tracer gas. The component to be tested is vacuum pumped and connected on one side to a mass spectrometer tuned to detect helium only. The component is normally exposed to atmospheric air, where generally speaking, there is a 5 ppm helium content. In other variants, a helium cylinder may be used so that a higher concentration of helium is allowed to leak through inside the component, and be detected by the mass spectrometer.
Helium-based leak detection systems can however be expensive, as a complete mass spectrometer carries a high cost, in addition to a vacuum pump, vacuum hardware, etc. Furthermore, helium suffers from a supply shortage and several attempts to replace helium in analytical systems have been documented.
The sensitivity and performance of known leak detection systems can also depend on the type of leak present in the component under test. Gas leaks may be classified under three types: orifice-type leaks, capillary-type leaks and permeation-type leaks.
A gas leak can generally be defined as the circulation of a gas from one area (for example, an inlet zone) to another area (for example, an outlet zone) and through a flow channel.
An orifice-type leak corresponds to a leak wherein the length of the flow channel is at most identical to its average diameter. Typically, orifice-type leaks can appear through the wall of a vessel or gas canister, tubing or fitting with inadequate sealing area, etc. Gases of low molecular size, like hydrogen, flowing easily through the orifice channel may be unsafe to use for detecting this type of gas leak.
A capillary-type leak corresponds to a leak wherein the length of the flow channel is much longer than its average diameter. Capillary-type leaks can appear in various valve configurations including globe, ball, butterfly, gate, etc. Capillary-type leaks can also appear through fittings, generally because they are not properly tightened or because the surface of the fitting wall is porous or scratched. Gases of low viscosity flow more easily through capillary channels.
A permeation-type leak corresponds to a leak wherein the flow channel is created by diffusion of gas molecules through an interface. Usually, gas molecules will move from a high concentration zone to a low concentration zone across the interface. For example, permeation-type leaks can appear in valves under high pressure through plastic or polymer sealing device, like gaskets and O-rings. It can also appear through thin metal walls and membranes. Gas permeation may be influenced by temperature and high pressures.
Leak detection systems and method should take under consideration the type or types of leaks to be detected. It would also be advantageous to provide such systems and method which enable the detection or different types of leaks.
There is thus a need for a technology that overcomes at least some of the drawbacks of what is known in the field.